This is a four-year, longitudinal, developmentally oriented nosologic study of childhood depression with youngsters aged 8-13 years. A structured clinical Interview Schedule for Children will be used to facilitate reliable psychiatric assessment. It is posited that the child's stage of cognitive development will mediate the clinical expression of the disorder. A three-index (three-task) measure of cognitive development has been devised which consists of a Piagetian task and two tasks of social (intra- and interpersonal) cognition. Stage of pubertal development will also be determined. It is hypothesized that a developmental framework may clarify the confusing phenomenological picture of childhood depression which currently dominates the literature. A longitudinal sequential design will be used to validate the concept of childhood depression and the developmentally oriented nosology. A depressed cohort of 120 children will be selected based on symptom criteria derived from the literature on which there was high "expert agreement". They will be obtained from Pittsburgh Child Guidance and from an outpatient service of Children's Hospital of Pittsburg. These children will be reevaluated at 2- 6- 12- 18- and 24-months after study entry. The depressed cohort will be contrasted with an equated sibling comparison group of 50 nondepressed Ss reassessed at 12- and 24-months. The repeated comprehensive assessment of the child through clinical, self- and parental rating and pediatric evaluation, the evaluation of parental psychiatric status through clinical- and self-ratings and determination of familial psychiatric history will facilitate a detailed characterization of the cohorts. The feasibility of the study is supported by extensive pilot work. The study will contribute to a developmentally oriented nosology of childhood depressive disorders and may provide some evidence as to appropirate treatment approaches for such youngsters.